An Optical Transport Network (OTN) is comprised of a plurality of switch nodes linked together to form a network. The OTN includes an electronic layer and an optical layer. The electronic layer and the optical layer each contain multiple sub-layers. The optical layer provides optical connections, also referred to as optical channels or lightpaths, to other layers, such as the electronic layer. The optical layer performs multiple functions, such as monitoring network performance, multiplexing wavelengths, and switching and routing wavelengths. In general, the OTN is a combination of the benefits of SONET/SDH technology and dense wavelength-division multiplexing (DWDM) technology (optics). OTN structure, architecture, and modeling are further described in the International Telecommunication Union recommendations, including ITU-T G.709, ITU-T G.872, and ITU-T G.805, which are well known in the art.
The construction and operation of switch nodes (also referred to as “nodes”) in the OTN is well known in the art. In general, the nodes of an OTN are generally provided with a control module, input interface(s) and output interface(s). The control modules of the nodes in the OTN function together to aid in the control and management of the OTN. The control modules can run a variety of protocols for conducting the control and management of the OTN. One prominent protocol is referred to in the art as Generalized Multiprotocol Label Switching (GMPLS).
Generalized Multiprotocol Label Switching (GMPLS) is a type of protocol which extends multiprotocol label switching (MLS) to encompass network schemes based upon time-division multiplexing (e.g. SONET/SDH, PDH, G.709), wavelength multiplexing, and spatial switching (e.g. incoming port or fiber to outgoing port or fiber). Multiplexing is when two or more signals or bit streams are transferred over a common channel. Wave-division multiplexing is a type of multiplexing in which two or more optical carrier signals are multiplexed onto a single optical fiber by using different wavelengths (that is, colors) of laser light.
RSVP and RSVP-TE signaling protocols may be used with GMPLS. To set up a connection in an Optical Transport Network, nodes in the Optical Transport Network exchange messages with other nodes in the Optical Transport Network using RSVP or RSVP-TE signaling protocols. Resources required for the connection are reserved and switches inside the network are set. Information sent by signaling protocols are often in a type-length-value (TLV) format. The same protocols may also be used to take down connections in the Optical Transport Network when the connections are no longer needed.
OSPF and OSPF-TE routing and topology management protocols may also be used with GMPLS. Under OSPF protocols, typically each node in an Optical Transport Network maintains a database of the network topology and the current set of resources available, as well as the resources used to support traffic. In the event of any changes in the network, or simply periodically, the node floods the updated topology information to all the Optical Transport Network nodes. The nodes use the database information to chart routes through the Optical Transport Network.
Traffic Engineering (TE) is a technology that is concerned with performance optimization of operational networks, such as OTNs. In general, Traffic Engineering includes a set of applications, mechanisms, tools, and scientific principles that allow for measuring, modeling, characterizing and control of user data traffic in order to achieve specific performance objectives.
Current Traffic Engineering practices have been utilized to increase the data rates in networks. However, future information transport systems are expected to support service upgrades to data rates of one terabyte per second (Tbps) and beyond. To accommodate such high rates in transport network architectures, multi-carrier Super-Channels coupled with advanced multi-level modulation formats and flexible channel spectrum bandwidth allocation schemes may be utilized. In this instance, spectrum allocated to particular Super-Channels is very flexible. Super Channels carry data using optical carriers which are bands within the optical spectrum. In other words, the Super Channels can be accommodated by combining several optical carriers together. In these types of networks, a routing and spectrum assignment (RSA) algorithm may be used to setup the Super Channels. The RSA algorithm considers the spectrum continuity and optical carrier consecutiveness constraints while assigning a spectrum path (SP) to any incoming connection. The spectrum continuity constraint requires continuous availability of optical carriers along an optical route (if no frequency converter is provided). The optical carrier consecutiveness constraint requires that the optical carriers assigned to any Super Channel should be consecutive in spectrum domain. Due to the additional constraints, the RSA problem in optical networks is even more challenging. The dynamic RSA problem can also be challenging due to the random traffic arrival/departure and the fluctuation of the traffic demands over time.
In optical networks with dynamic traffic, the frequent set-up and tear down of optical routes can lead to significant fragmentation of spectral resources. Due to the spectrum continuity and optical carrier consecutiveness constraints, several spectrum slots in between connections remain unused thereby reducing the amount of data that can be transported within the optical network. In particular, these spectral fragments of unused spectrum fragments may be small, scattered and may not be enough to establish new optical routes because of aforementioned constraints in optical networks. As a result, the spectral fragments increase the maximum sub-carrier index (MSI) in each fiber or decrease the probability of finding sufficient contiguous sub-carriers for new optical routes. Requests for new optical routes are then forced either to utilize more spectrum in the fiber or are blocked even though sufficient spectrum are available. Hence, the spectral fragments produce a significant amount of waste of the expensive spectral resources which may lower spectral usage and increase blocking.
Conventional techniques for solving this problem include spectral defragmentation algorithms that reconfigure existing connections with the goal of consolidating the spectrum allocation. The scattered and fragmented spectrum slots can be consolidated by either shifting the existing optical carrier allocation between one node pair to a different group of optical carriers, assigning a new route to an existing connection, or both while maintaining the optical carrier consecutiveness and spectrum consecutiveness constraints. Network administrators can perform the spectrum defragmentation on a periodic manner to consolidate spectrum or on demand when the links' optical carrier index increases beyond a threshold (indicating the potential blocking of future connection requests).
There is a need to reduce fragmentation in optical networks to enhance spectral usage and the amount of data traffic transported by the optical network. The present disclosure addresses this need with methodologies and systems that reduces the amount of fragmentation by generating allocation recommendations that, if followed by a network administrator, reduces the fragmentation of the optical network when the network administrator is processing requests for new optical routes.